1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, particularly, to a method of manufacturing a semiconductor device comprising a step of forming a pattern on a working film to be processed by using a mask material and a resist pattern.
2. Description of the Related Art
In the manufacturing method of a semiconductor device, a series of process steps comprising a step of depositing a film to be processed on a silicon wafer and q step of patterning the deposited film in a desired pattern are repeatedly carried out. In patterning the deposited film, a resist film is formed by depositing a photosensitive substance, which is generally called a resist, on the deposited film, followed by exposing a predetermined region of the resist film to light. Then, the light-exposed portion or the unexposed portion of the resist film is removed by a developing treatment so as to form a resist pattern. Further, the film to be processed is subjected to a dry etching with the resist pattern used as a mask so as to obtain a pattern of a desired shape.
An ultraviolet light such as a KrF excimer laser or an ArF excimer laser is used as the light source in the light exposure process in view of the throughput. However, since the required resolution has been rendered smaller than the wavelength of the exposing light in accordance with miniaturization of the LSI, the latitudes in the light exposure process such as the exposure latitude and the focus latitude have become insufficient.
In order to make up for these process margins, it is effective to decrease the thickness of the resist film for improving the resolution. In this case, however, a new problem is generated that it is impossible to ensure the thickness of the resist film required for the etching of the film to be processed.
To overcome the problems pointed out above, a pattern transfer process is proposed in, for example, Japanese Patent Disclosure (Kokai) No. 2001-272797 and Japanese Patent Disclosure No. 2002-305187. To be more specific, it is proposed that a mask material and a resist film, which are resistant to etching, are formed successively on the film to be processed, followed by applying a light exposure treatment and, then, a developing treatment to the resist film so as to form a resist pattern. Further, the film to be processed is patterned by using as an etching mask a mask material pattern obtained by transferring the pattern of the resist pattern to the mask material.
According to the method proposed in the prior art quoted above, it is possible to pattern the film to be processed with a high accuracy even if the thickness of the resist film is decreased such that the resist pattern disappears during the etching process because the mask material pattern is resistant to the etching during the etching process of the film to be processed.
It is desirable for the mask material to be provided by a material that can be formed into a film by a coating method because the process cost is low. It is also desirable for the mask material film to be peeled easily with oxygen ashing. An organic material containing a large number of carbon atoms, which is unlikely to be sputtered and resistant to the etching, is used as such a mask material.
However, in the case of using an organic material, particularly, an organic material having a high carbon content, the mask material pattern is ruptured during the etching process of the film to be processed, with the result that it is difficult to transfer the pattern of the resist pattern onto the film to be processed.